In a message dated 1/24/97 4:43:23 PM, kocher+@andrew.cmu.edu (James M
Kocher) wrote:
>I understand that mustard plants can be used to soak up toxins, such as
>lead, from the soil. The plants are then destroyed and not composted of
>course. It is alo my understanding that fruit in general does not
>absorb toxins readily from the soil and thus can be planted safely in
>such areas.
>
>What other plants can be used to absorb toxins, and what other plants
>are safe to plant and eat from in such areas?
>
>Jim Kocher-Hillmer, Pittsburgh PA USA
Carrots are routinely used to soak up accumulated agricultural toxins in
farming, I'm told. They are disposed of by being sold. Water hyacinth has
been successfully used to extract heavy metals from sewage to such an estent
that the metals can be usefully recovered from the ash. (I imagine that the
incineration process has several environmental costs, however.)
The issue of toxic metals is not simple. You can't destroy lead by
"destroying" the mustard plants. Lead is a very stable element.
I suspect that vegatively removing poisons from soil is a false solution as
we still have the poisons in our organic residue. Either they go back to the
same soil, they go into different soil, they get dumped into water, or in
some cases they get released into the air (as pyrolytic gases or ash
particles). Moving toxins around may be waste of usful resources, and
obviously has to result in more pollution.
Unfortunately, there is no easy way to say what does work. I keep thinking
of putting the ash of such concentrators at the bottom of strip mines or
under new highways where they won't be released until future generations tear
up the roads and I just don't feel good about the options. Moreover, I'm not
sure that we can remove useful proportions of poison from soil this way,
though surely it may be possible. If you get a lot of lead in a mustard
leafe, the entire mustard crop may still take out way less than one percent
of the lead in the soil. Moreover, the more you take out, the slower the
rate of uptake.
In urban soils, we recommend a combination of three strategies, to be
determined by circumstances and the people on site. 1) Get soil pH to about
6.5 to 7. Some, but not all heavy metals are less available to plants at this
range. 2) Increase organic content of soil. This helps tie up metals and
organic poisons have more breakdown pathways. Research has shown that
agricultural pesticides, other than the elementals such as arsonate of lead,
which are no longer widely used, break down more quickly organically managed
soils than in soils managed by the methods of mainstream industrial
agriculture. Of course, agricultural chemicals have changed by now and there
is no guarantee that this will continue to be the case, but since the trend
has been to less persistent chemicals, that's the way to bet. 3) Grow crops
known not to take up toxins. Different "experts" arrange their lists
differently. Much depends on whether a lot of your pollution includes a
sizeable input from atmospheric pollution.
There is good (unpublished, to my knowledge) evidence that certain parts of
plants accumulate toxins. For example the skins of some root crops should be
saved and the skin of others can be thrown away as containing most of the
toxins. Unfortunatly, I ran across this evidence decades ago and I neglected
to make notes. What is needed here is good spectrographic analysis of crops,
species by species, variety by variety, and edible part by edible part.
In the meanwhile, use the published data from work closest to where you live.
I'm sure that variations in soils and climates also play a role in toxin
uptake.
Finally, in really "hopeless" urban situations, we recommend soil-less
gardening techniques and/or creating a new soil zone deep enough so that
plant uptake from the soil below will be minimal. We intend to to a survey
of soil-less techniques in an upcoming issue of our journal, The
International Permaculture Solutions Journal, probably in the issue after
next. (Next issue follows on our soils issue and introduces design factors
in a theme "Curves in the gardenn".)
If you don't live where glaciers periodically come down and renew the soil,
you may be looking at damage that will take hundreds of thousands of hears to
remedy, regardless of what you do. Like the feller said, observing a kid
trying to put a road kill back together, "That's going to take a while."\
Good luck. It is a serious problem without simple solutions.
For Mother Earth, Dan Hemenway, Yankee Permaculture Publications (since
1982), Elfin Permaculture workshops, lectures, Permaculture Design Courses,
consulting and permaculture designs (since 1981), and now correspondence
permaculture training by email. Copyright, 1996, Dan & Cynthia Hemenway, P.O.
Box 2052, Ocala FL 34478 USA YankeePerm@aol.com
We don't have time to rush.